CCTV images of the attack showed the pensioner falling to the pavement after being hit in head by two hooded teens. The 67-year-old hit his head on the pavement and suffered irreparable brain damage. He died one week later in hospital.

Elcock and Lyzai, both from Tooting, pleaded guilty to manslaughter and also admitted their parts in other so-called “happy slap” attacks that their gang had carried out in the run up to the fatal assault on Mr Haque.

Many of their assaults were filmed on mobile phones and appeared to primarily target elderly Asians in the Tooting area.

Murder charges were dropped in favour of the teens pleading guilty to manslaughter and actual bodily harm. Judge Martin Stephens, sitting at the Old Bailey, sentenced Elcock to four and a half years and Lyzai for three and a half years. But he admitted that his sentencing options were “very limited” because of the defendants’ young ages.

Both killers will be released on licence after serving just half their sentences, minus the year they have already been in custody, which means they will be free within a year and a half.

A 15-year-old youth, who formed part of the same gang but cannot be named for legal reasons, was also detained for six months after admitting his part in a previous attack on an elderly couple which was carried out with Elcock.

"I thought justice has not been served today,” he said. “I have been really let down. The CPS really need to buck up their ideas because people are getting away with murder. My father died. It's a disgrace."

Judge Stephens took the unusual step of lifting restrictions of the press naming Elcock and Lyzai as a warning to others “who may be tempted to indulge in such appalling behaviour".

In sentencing the pair he said: "The attacks were entirely gratuitous and done without thought for your victims.

"The blow or blows launched on [Mr Haque] led directly to his death. He fell to the ground, cracked his head, and suffered irreparable brain damage."

"As a result of your so-called bit of fun he was deprived of a full and contented life and his family of a devoted, inspiring and beloved father and grandfather."

Mr Haque's son Arfan, 35, said outside court: "I thought justice has not been served today. I have been really let down.

"The CPS really need to buck up their ideas because people are getting away with murder. My father died. It's a disgrace."

He had earlier told the court in a statement: "It is tragic that he died in the way he did because he was a very peaceful man."

He said his daughter had been traumatised by what happened because she had a special relationship with her grandfather.

Both killers will be released on licence after serving half their sentences, minus nearly a year they have already been in custody, while the 15-year-old has effectively completed his sentence already.

The judge said his powers of sentence in relation to the assaults were "very limited" because of the defendants' ages.